Composites such as FRP (Fiber Reinforced Plastic) including reinforcement fiber are lightweight and have high strength. Thus, the composites are increasingly used for components of an airplane, an automobile, a ship, a railroad vehicle and the like.
One method of this type for manufacturing these composites is an autoclave molding method where a plurality of prepreg materials formed by impregnating reinforcement fiber sheet with resin are stacked, covered by a bag film to be vacuumed, and then pressurized and thermally cured by an autoclave. Another method is a vacuum impregnation method where a mold release film and a mesh sheet are arranged on reinforcement fiber sheets stacked on a mold and they are covered by a bag film to be vacuumed while liquid resin is injected inside the bag film to cure.
In these methods for manufacturing the composites, a major part of the stacking operation of base material sheets made of materials such as prepreg materials and reinforcement fiber sheets is manually done. Thus it takes a lot of time and is not effective. In view of improving the operation efficiency and the product quality, a variety of apparatuses for stacking the base material sheets have been proposed.
Disclosed in Patent Literatures 1 and 2 is an apparatus for stacking roving materials formed by impregnating the reinforcement fibers with resin. This apparatus winds the roving material drawn from a supply unit around a stacking roller, and rolls the stacking roller along the mold while pressing the roving material against the mold so as to stack the roving material on the mold. Further, disclosed in Patent Literature 3 is an apparatus for stacking composite material tapes in a continuous manner, where a composite material tape supplied from a material supply reel is pressed onto a stacking member by a roller so as to stack the composite material tapes in a continuous manner.
As a wind turbine blade for instance, there is a blade mold 70 having a shape of a saddle as shown in FIG. 9A. Herein, FIG. 9A and FIG. 9B are illustrations of a conventional method for manufacturing a fiber-reinforced base material. FIG. 9A is a perspective view of the base material sheets stacked on the mold using the base material roll. FIG. 9B is an enlarged cross-sectional view of a section B of FIG. 9A. This blade mold 70 has a double-curved surface shape curving in X direction, i.e. a width direction as well as in Y direction, i.e. a longitudinal direction, a sheet supplying direction of the base material sheet 72. In this case, the base material roll 71 around which the base material sheet 72 is winded rolls in the longitudinal direction of the mold to extend the fiber 73. However, the mold 70 having a double-curved surface shape changes in length depending on a position in the width direction. Thus, by arranging the base material sheet 72 along the mold 70, a wrinkle 80 occurs as shown in FIG. 9B. Particularly, in the case where the fibers 73 are unidirectional reinforcement fibers arranged along the sheet-supplying direction, the unidirectional reinforcement fiber has poor deformability on the mold 70 in in-plane direction unlike cloth fabric and thus it is difficult to fit the unidirectional reinforcement fiber along the curved surface of the mold 70.
Referring to FIG. 10A and FIG. 10B, generation of the wrinkle 80 is described in details. When a flat base material sheet 72 is pressed onto the mold 70 having the saddle shape, the wrinkle 80 occurs in the base material sheet 72. Further, the base material sheet 72 is a unidirectional reinforcement fiber whose fibers are arranged unidirectionally along the longitudinal direction of the mold 70.
As shown in FIG. 10A, the base material sheet 72 is arranged such that its fiber direction coincides with the longitudinal direction of the mold 70. The base material sheet 72 is pressed onto the mold 70 from directly above so as to fit two sides A′D′, B′C′ of the base material sheet 72 to arcs AD, BC of the mold 70 in the width direction.
FIG. 10B shows a side view of the mold 70 and the base material sheet 72 of FIG. 10A. As shown in a bottom drawing of FIG. 10B, a surface ABCD of the mold 70 (see FIG. 10A) is formed by the arcs AB, DC such that the surface is concave from the arcs AB, DC toward the arc EG. When the mold 70 is viewed from the side, the arc EG is located lower than the arcs AB, DC. Further, the arc length EG is shorter than the arc lengths AB, DC. The surface ABCD of the mold 70 increases in arc length with distance from the arc EG toward the arc AB or DC. In contrast, the surface A′B′C′D′ of the base material sheet 72 is flat and thus two sides A′B′ and D′C′ have the same length as a distance between middle points E′G′ in the longitudinal direction. The middle points E′, G′ are located in the middle between the two sides A′B′ and D′C′.
Therefore, the length between the longitudinal middle points E′G′ of the base material sheet 72 is greater than that of the arc EG of the mold 70. When the base material sheet 72 is stacked on the mold 70 to fit the sides A′D′ and B′C′ of the base material sheet 72 to the arcs AD and BC of the mold 70, the wrinkle 80 occurs near a part between widthwise middle points F′H′. The widthwise middle points F′, H′ are located in the middle between two sides A′B′ and D′C′ of the base material sheet 72 in the width direction as shown in FIG. 10B. As described above, the surface ABCD of the mold 70 increases in arc length with distance from the arc EG toward the arc AB or DC. This contributes to generation of the wrinkle 80. The number of wrinkles 80 occurring near the widthwise middle points F′H′ of the base material sheet, decreases toward the side A′B′ or the side D′C′ of the base material sheet 72.
Patent Literature 4 discloses an apparatus for stacking the base material sheet without causing wrinkles. The disclosed apparatus is provided with a means for drawing the base material sheet onto the mold and a means for pressing the base material sheet onto the mold. The apparatus supplies the base material sheet onto the mold while loading a tensile force on the base material by the pressing means which is smaller in width than the base material sheet. Upon receiving the tensile force, the base material sheet deforms in the direction of the tensile force so that the base material sheet can be stacked along the shape of the mold without causing wrinkles.